Generally, the present invention relates to the field of bill and currency note validation, and in particular to detecting and determining the authenticity of watermarks and security threads contained in currency notes.
In general, it is fairly easy to create a color copy of any currency using commonly available color printers. These printers are easily accessible and available worldwide at low cost and combining them with a color scanner and personal computer (PC), potentially permits a counterfeit currency note or bill to be readily made in a few minutes, and replicated at high speed. In addition, the expanding availability of high quality color copiers eliminates the need for a PC and scanner to replicate a currency note.
In an effort to quash the introduction of counterfeit notes, many countries, including the United States, now feature either a watermark, a security thread or both in one or more denominations of currency. These security features are used to give the receivers a means to optically verify a particular note's authenticity. Both features are being incorporated in notes worldwide on an increasing basis as the capability of technology to produce high-quality counterfeit copies of notes increases.
In the early 1990's, the United States Treasury Department, for example, added a plastic security thread to most of the United States of America's denominations. This thread is embedded in the paper on which the money is printed, and includes a textual description of the denomination, e.g. $100 USA. Continued advancement of counterfeiting techniques have forced the Treasury Department to redesign many notes with such features as a more advanced security thread and a watermark.
Most security threads are fairly narrow (less than 0.100 inches wide) and generally run across the short dimension of the note. Threads are made of various materials, including plastics, metallized plastics and magnetic elements. These threads may be fully embedded in the notepaper, or may be `weaved` with parts of the thread exposed above the paper surface. As in the United States, some threads are inscribed with the denomination of the note and often are located in various longitudinal positions in the note. To authenticate the note, an individual usually holds it in front of a light source to verify the existence of the thread and oftentimes read the denomination inscribed on the thread.
Currency paper watermarks are finely detailed images similar in resolution to the printing on the surface of the note. The images are produced through a combination of chemical treatment and/or pressure that causes variations in the distribution of fibers in the watermark area. These variations change the way light is absorbed and reflected causing a characteristic `shadow` or dim image. In addition, the watermark may be partially or completely overlaid by printing on the surface of the note. For this reason, watermarks are often difficult to detect when observed head on, and therefore an individual typically illuminates the area from behind and looks for the image. Illuminating the note in this manner allows the required variations to be observed, thus allowing the individual to verify the authenticity of the note.
While the introduction of such security features are essential in deterring the passing of counterfeit currency notes and other documents, they are only as effective as the individual evaluating them. If, for example, an individual has neither the time or the inclination to verify the existence of these features their presence or absence in a particular currency document will not prevent a false note from being passed. This problem is most significant and apparent in businesses handling a large volume of paper money transfers. Environments such as casinos, currency exchanges, banks, etc., require a more automated and reliable way of preventing and detecting counterfeit currency introduction.
To accommodate these high volume environments, automatic verification devices such as bill note validators have been developed. For example, Haslop (U.S. Pat. No. 4,296,326) discloses an apparatus and method for detecting a genuine watermark, utilizing ultraviolet radiation. Haslop discloses measuring the fluorescence characteristics of a note by subjecting it to ultraviolet radiation. This device requires high powered light source to produce the ultraviolet radiation.
Ohtombe (U.S. Pat. No. 4,524,276) discloses an apparatus for optically detecting the presence of a metallic or non-metallic security thread in a bank note. The reference discloses an infrared emitter and multiple filtered detectors to test the transmissive characteristics of the embedded thread. Similarly, Crane (U.S. Pat. No. 4,980,569) discloses a device that measures the reflected and transmitted light from a note containing a thread. The device attempts to detect the counterfeiter's method of applying a thread on the surface of the paper by measuring the high reflectivity of a thread mounted in this manner.
Finally, Ebstein (U.S. Pat. No. 5,468,971), discloses an apparatus that detects the images of fine writing embedded within the security thread. In practical terms, this requires an intense light source and a high resolution set of sensors, as the resolution of the print is very high, on the order of 0.001" in width.
The prior art fails to provide a solution that detects and verifies the presence of a security thread and a watermark in one apparatus. Further, various features of the prior art such as high intensity light sources and high powered components make them incompatible with efficient and cost effective design constraints. For this reason, there is a need for a solution that can detect the presence of security features in a currency note, while still maintaining a low-cost and efficient component structure. In addition, the solution should provide a single design for determining the presence of both a watermarks and security threads.